3D Printing Hydrogel-Based Soft and Biohybrid Actuators: A Mini-Review on Fabrication Techniques, Applications, and Challenges

Abstract

Stimuli-responsive hydrogels are candidate building blocks for soft robotic applications due to many of their unique properties, including tunable mechanical properties and biocompatibility. Over the past decade, there has been significant progress in developing soft and biohybrid actuators using naturally occurring and synthetic hydrogels to address the increasing demands for machines capable of interacting with fragile biological systems. Recent advancements in three-dimensional (3D) printing technology, either as a standalone manufacturing process or integrated with traditional fabrication techniques, have enabled the development of hydrogel-based actuators with on-demand geometry and actuation modalities. This mini-review surveys existing research efforts to inspire the development of novel fabrication techniques using hydrogel building blocks and identify potential future directions. In this article, existing 3D fabrication techniques for hydrogel actuators are first examined. Next, existing actuation mechanisms, including pneumatic, hydraulic, ionic, dehydration-rehydration, and cell-powered actuation, are reviewed with their benefits and limitations discussed. Subsequently, the applications of hydrogel-based actuators, including compliant handling of fragile items, micro-swimmers, wearable devices, and origami structures, are described. Finally, challenges in fabricating functional actuators using existing techniques are discussed.

Recent advances in the 3D printing of electrically conductive hydrogels for flexible electronics

“…Meanwhile, the heterogeneous stimulation refers to the response regarding to the external environment variation, such as humidity, pH, optical, electrical or thermal stimuli. 140 Based on different mechanisms, the hydrogel actuation could be categorized into osmotic actuation, 141 cell-powered actuation, 142 pneumatic/hydraulic actuation, 143 magnetic actuation 144 and acoustic actuation 145 . Different 3D printing techniques have been employed to fabricate the hydrogel actuators.…”

Smart 3D Printed Hydrogel Skin Wound Bandages: A Review

“…The study discussed composite, natural and synthetic hydrogels. W. Sun et al reviewed 3D printing technology used for printing hydrogel actuators [ 33 ]. The actuation mechanisms, including pneumatic, hydraulic, ionic, dehydration-rehydration, and cell-power actuation, were addressed.…”

Continuous fiber extruder for desktop 3D printers toward long fiber embedded hydrogel 3D printing

“…Recent advances in hydrogel 3D printing have enabled the fabrication of hydrogel structures with complex 3D geometry and a wide range of applications, including tissue engineering [2] , soft robotics [3] and drug delivery [4] . Common hydrogel 3D printing techniques include inkjet-based, laser-based and extrusion-based printing, among which extrusion-based printing is often considered attractive to the 3D printing community due to a large selection of low-cost and open-source software and hardware [5] . However, many hydrogel inks, e.g., collagen and alginate, are so soft that the newly printed structures can not support their own weight and yield inferior geometric fidelity.…”